Graphene has attracted much excitement in academic and industrial research. Its 2D nature gives cause to unique electronic properties. The monolayer nature lets π-conjugated system entirely exposed to external influence of its surroundings. While this is a general problem in controlling its properties, doping of graphene is much sought for numerous electronic and photonic applications. Schedin et al Nature Materials 2007, 6, 652, showed in ultra high vacuum conditions that adsorption events of molecules to graphene changed its electronic properties. This finding led to intensive research on the chemical induced doping of graphene for numerous applications.
While for blockbuster applications such as displays permanent changes in the charge carrier density increases the conductivity the potential lies in opening up a band gap to create all carbon based electronics. For sensing changes the electronic properties are to be monitored electrically in chemical field effect transistors or chemical resistors (ChemFETs and chemiresistors) sensors.
There is a worldwide demand for sensors in particular for stand-alone and mobile systems for environmental, air quality and safety control. The most established techniques such as mass spectrometry, electrochemical, infrared or metal oxide sensors suffer either from limited sensitivity, high power consumption, high production cost or inability to miniaturise. These challenges can be overcome in chemiresistors where with the discovery of nanomaterials such as nanotubes and -wires which possess high surface-to-volume ratio detection levels of the order of ppm or sub-ppm have been reported, as disclosed in Kauffman, D. R.; Star, A. Analyst 2010, 135, 2790. This matches the sensitivity of conventional metal oxide film sensors at room-temperature, thereby avoiding energy intensive operation at elevated temperatures. However a problem exists over scalability and reproducibility of these devices.
A number of groups have shown graphene as sensors for gases and liquids. Besides having high sensitivity graphene is potentially easy to manufacture and chemically robust, however device reliability is heavily dependent on the quality of the graphene and selectivity hinges on contact engineering and passivation of the channel.
It is therefore an object to provide an improved sensor device to overcome at least one of the above mentioned problems.